One method to control intake and exhaust valve operation during engine operation is described in U.S. Pat. No. 5,765,514. This method provides a method of starting an engine with electromechanical valves. This method provides for an injection sequence for the cylinders that is initialized when a first crankshaft pulse is generated after generation of a first signal pulse representing crankshaft rotation through 720 degrees. The injection sequence and crankshaft position sequence correspond to the position of each cylinder, whereby the opening/closing timing of each intake valve and exhaust valve can be controlled. The cylinders are set to the exhaust stroke, suction stroke, compression stroke, and explosion stroke, respectively.
Once the above-mentioned method has set the stroke of each cylinder, timing of valve opening and closing is determined by retrieving a map based on accelerator pedal position and engine speed. Finally, a further valve timing adjustment is made to correct for air-fuel errors and valve operating conditions. Specifically, valve temperature and power supply voltage are referenced to correct valve opening and closing times.
The inventors herein have recognized that the before-mentioned approach can have several disadvantages. For example, the approach can adjust valve opening and closing times based on power supply voltage, but operating a valve at elevated temperatures may result in increased valve degradation. For example, insulation between valve windings may degrade if a valve is operated at elevated temperatures and with an increased amount of current. Therefore, adjusting valve timing and operating based on a temperature of a valve may be undesirable under certain circumstances. In addition, the method may not perform as desired if a valve has experienced degradation. For example, if a valve has increased or decreased impedance it may not open or close as desired.